Here's a thought experiment for you: Suppose someone releases a software package under "GPL v3 or later", with all its new requirements to prevent tivoization. They do this because they like the additional guarantees their software will remain free, and they really don't want their software tivoized.
Now the FSF releases the GPL v4 that reverts the changes in GPL v3, and reads identical to GPL v2.
Theoretically, the GPL v3 was similar in spirit to the GPL v2. So, this imagined GPL v4 should also be similar in spirit to GPL v3. Now what?
Really, the "or later" clause cedes an awful lot of control to the FSF. That's been my point all along. The punch line is that if you care that much about the specific semantics of the license that covers your code, you really shouldn't put a wildcard in the license that you don't control.